Method for Operating a Winding Device

ABSTRACT

A method for operating a winding device of a processing machine for processing a material web is disclosed. A winding device is provided for winding or unwinding the material web. The winding device is operated to specify a web tension, wherein a switch occurs from a first web tension specification procedure to a second web tension specification procedure during the processing of the material web.

The present invention relates to a method for operating a winding deviceof a processing machine for processing a material web and to anassociated computing unit.

Although in the following text reference will primarily be made toprinting presses, the invention is not restricted thereto but instead isdirected to all types of processing machines in which a product web ormaterial web is processed. However, the invention can be used inparticular in printing presses such as newspaper printing presses,commercial printing presses, gravure printing presses, in-lineflexographic printing presses, packaging printing presses or valuabledocument printing presses and also in processing machines such asbag-making machines, envelope-making machines or packaging machines. Thematerial web can be formed from paper, fabric, paperboard, plastic,metal, rubber, in the form of film or foil and so on.

PRIOR ART

In material web processing machines, winding devices are used optionallyas winders or unwinders. A winding device normally comprises at leastone driven shaft, for example a winding shaft of a center winder, adrive shaft of a circumferential winder, a pull roll or the like, anassociated actuating or controller function, for example in a motioncontrol system or memory-programmable controller (PLC) and, ifappropriate, measuring elements for determining the web tension. Thewinders are normally operated in such a way that a web tension isimpressed on the material web, both control and also merely setting ofthe web tension being used. In the prior art, different methods forcontrolling or setting web tension are known in the winders ofweb-processing machines.

For example, a dancer control system or else a dancer position controlsystem is used, in which the web tension is typically impressed on theweb by a gravitational force or pressure on the dancer. The object ofthe dancer position control system is to keep the dancer withinpredefined limits, the set point of the dancer position normally beingset to a central position. A dancer position control system is normallyused to compensate for sudden disturbances, non-roundness in the coil ornon-uniform web transport. A method or structure with a dancer positioncontroller is mostly used when the material web does not runcontinuously or sudden disturbances have to be compensated for. Inparticular in the case of a flying reel change, a dancer is usuallyimperative.

In addition, it is known to set or control the web tension by means oftensile force control of the driven winder shaft. In this case, thecontroller typically specifies either the drive torque or the rotationalspeed of the shaft. Control of the drive torque is expediently used inthe case of stiff material with a high modulus of elasticity, such aspaper, metal, whereas control of the rotational speed is expedientlyused in the case of elastic material, such as foil, film or fabric.Tensile force control, as compared with dancer position control, offersthe advantage of the ability to be implemented more simply and of lowerexpenditure on components.

Finally, feedback-free setting of the web tension, for example bysetting rotational speed or setting drive torque, is also known. Thesetting or open-loop control offers the advantage of simplicity, sinceno kinds of mechanism, such as dancers or force transducers, ormeasuring elements, such as dancer height measurement or forcemeasurement, are needed. However, it is relatively inaccurate, sincedisturbances are not registered and cannot be compensated for by acontroller.

The structure or method with tensile force control/setting is normallyused instead of dancer position control when a constantly running webtransport without great disturbances is to be expected.

The known methods are relatively inflexible and cannot easily be adaptedto changed conditions, for example of new material. In addition, in thecase of production in which a flying reel change is provided,complicated dancer position control is always needed.

DISCLOSURE OF THE INVENTION

According to the invention, a method for operating a winding device of aprocessing machine for processing a material web having the features ofpatent claim 1 is proposed. Advantageous refinements are the subjectmatter of the subclaims and of the following description.

ADVANTAGES OF THE INVENTION

The invention is based substantially on the finding that flexible webtension control or setting that can be adapted to the respectiveconditions can be provided for a winding device if a switch is madeonline, i.e. during the production, from a first web tensionspecification method to a second web tension specification method. Theterm “specification method” comprises both control and setting methods.

Therefore, for example by switching as a function of the material, thecontrol structure can be matched particularly well to the material webmaterial. In particular in the case of production with a flying reelchange, particular advantages can be achieved. Expediently, duringnormal production, web tension specification without a dancer is usedfor this purpose. A switch to dancer position specification is madebefore the reel change in order to be able to compensate particularlyeffectively for the disruption which is caused by the reel change. Aswitch back from the dancer position specification to the original webtension specification is finally made after the reel change has beencarried out.

Likewise, a switch from rotational speed specification to drive torquespecification can advantageously be made during a change to a materialwith a greater modulus of elasticity (stiffer material). A switch fromdrive torque specification to rotational speed specification isconversely made during a change to a material with a lower modulus ofelasticity (softer material). Thus, during a change in the material, therespectively optimal specification method, i.e. control or settingmethod, can be selected.

A computing unit according to the invention, e.g. a control device of aprinting press, is equipped, in particular by programming, to carry outa method according to the invention.

In addition, the implementation of the invention in the form of softwareis advantageous, since this permits particularly low costs, inparticular if an executing computing unit is used for further tasks andis therefore present in any case. Suitable data carriers for providingthe computer program are in particular floppy disks, hard drives, flashmemories, EEPROMs, CD-ROMs, DVDs and many more. Downloading a programvia computer networks (Internet, Intranet and so on) is also possible.

Further advantages and refinements of the invention can be gathered fromthe description and the appended drawing.

It goes without saying that the features mentioned above and those stillto be explained below can be used not only in the respectively specifiedcombination but also in other combinations or on their own withoutdeparting from the scope of the present invention.

The invention is illustrated in the drawing by using an exemplaryembodiment and will be described extensively below with reference to thedrawing.

FIGURE DESCRIPTION

FIG. 1 shows a winding device with a dancer position control system inschematic form.

FIG. 2 shows the winding device according to FIG. 1 after a switch to arotational speed specification method has taken place.

FIGS. 1 and 2 will be described conjointly and in an overlapping manner,the same elements being provided with the same designations. Shown inFIGS. 1 and 2 is a winding device 100 which, according to a preferredembodiment of the invention, can be operated using different web tensionspecification methods. The intention is to explain below how, forexample after a flying reel change, a switch is made from dancerposition specification, as illustrated in FIG. 1, to rotational speedspecification, as illustrated in FIG. 2.

The winding device 100 has a winding shaft 101, onto which a materialweb 102 is wound. It goes without saying that the invention can likewisebe used during an unwinding operation. The winding device 100 has adancer 110 for specifying a web tension and a force transducer 120 formeasuring the web tension. The web tension value measured by the forcetransducer 120 is transmitted to a control device 130, which is providedfor web tension control. The control device 130 activates a dancer drive111 which exerts a specific pressure on the dancer 110 pneumatically,for example. The dancer position is detected by a dancer positioncontroller 131, which specifies and controls the rotational speed or thedrive torque of the drive shaft 101 on this basis. It goes withoutsaying that the web tension controller 130 and the dancer controller 131can also be embodied in a common control device.

It can be seen that the dancer position control system requires amultiplicity of elements and is therefore to be viewed asover-dimensioned for conventional operation. The substantial advantageof the dancer position control system consists in the possibility, inparticular during a flying reel change, of intercepting the disturbancein the web tension behavior, brought about by the reel change, throughthe web material stored in the dancer, and of avoiding damage to thematerial web. After the reel change has been carried out, rotationalspeed control is often more practical. According to the presentembodiment of the invention, after the reel change has been carried out,a switch is therefore made to rotational speed or drive torquespecification (control), as illustrated by using FIG. 2.

During the online switchover to dancer-free operation, first of all thedancer position setpoint is set to a value which corresponds to thedancer stop. As illustrated in FIG. 2, the dancer 110 is, for example,fixed at the upper stop. After the dancer stop has been reached, a startis made on the structure or method switch. At the same time, the dancerpressure is reduced since, following the switchover, the web tension isno longer specified by the dancer pressure. After the switch, the webtension controller 130 will control the rotational speed or the driveelement of the shaft 101 on the basis of the web tension measured by theforce transducer 120.

The structure switch during the production operation is expedientlycarried out in such a way that, at the time of the switch, no stepsoccur in the control loop. For example, in the case of a PID controllerand in the case of a force transducer structure with specification of adrive torque, the instantaneous drive torque is read and the integralterm of the controller is predefined in such a way that, following theswitch, the same reference torque appears at the controller output. Inthe case of a force transducer structure with pre-definition of a driverotational speed, the instantaneous drive rotational speed isexpediently read and the integral term of the controller is predefinedin such a way that, following the switch, the same reference rotationalspeed appears at the controller output. A switch to dancer positionspecification can also be carried out in a comparable way by theintegral term being predefined in accordance with the current rotationalspeed.

During a switch from rotational speed specification to dancer positionspecification, the dancer position setpoint can be set to the dancercenter, for example, and as the switch in the control is made, thedancer pressure can also be set appropriately at the same time.Alternatively, instead of moving to the dancer stop, mechanical fixingof the dancer, for example by means of a mechanical brake, at anotherpoint, for example at the dancer center, can also be carried out. Inthis refinement, the dancer advantageously does not first have to bemoved to the stop and later moved back into the central position.

1. A method for operating a winding device of a processing machine forprocessing a material web, comprising: (a) processing the web materialso as to wind up or unwind the material web with a winding device, (b)operating the winding device so as to specify a web tension during theprocessing step, (c) during the processing step, switching from a firstweb tension specification method to a second web tension specificationmethod.
 2. The method as claimed in claim 1, wherein the first and/orsecond web tension specification method is selected from the groupcomprising control and setting of a dancer position, of a rotationalspeed and of a drive torque.
 3. The method as claimed in claim 1,further comprising: (d) carrying out a flying reel change, and whereineach of steps (a), (b), and (c) are carried out before step (d).
 4. Themethod as claimed in claim 3, wherein: the second tension specificationmethod is a a dancer position specification method, and step (c) iscarried out before step (d).
 5. The method as claimed in claim 3,wherein: the second tension specification method is a dancer positionspecification method, and step (c) is carried out after step (d).
 6. Themethod as claimed in claim 5, wherein the dancer is fixed before step(c).
 7. The method as claimed in claim 1, further comprising: (d)carrying out a change in the material, and wherein each of steps (a),(b), and (c) are carried out before step (d).
 8. The method as claimedin claim 7, wherein: the second tension specification method is arotational speed specification method, and step (c) is carried outduring a change to a material with a lower modulus of elasticity.
 9. Themethod as claimed in claim 7, wherein: the second tension specificationmethod is a drive torque specification method, and step (c) is carriedout during a change to a material with a greater modulus of elasticity.10. A computing unit configured to carry out a method for operating awinding device of a processing machine for processing a material web,comprising: (a) processing the web material so as to wind up or unwindthe material web with a winding device, (b) operating the winding deviceso as to specify a web tension during the processing step, and (c)during the processing step, switching from a first web tensionspecification method to a second web tension specification method. 11.The method as claimed in claim 1, further comprising: (d) carrying out—aflying reel change, and wherein each of steps (a), (b), and (c) arecarried out after step (d).
 12. The method as claimed in claim 1,further comprising: (d) carrying out a change in the material, andwherein each of steps (a), (b), and (c) are carried out after step (d).